1. Field of the Invention
The present invention relates to catalyst compositions, and more particularly, to a catalyst composition for preparing hydroxylamine.
2. Description of the Related Art
Industrial production of hydroxylamine is usually accomplished by coupling with other processes conducted sequentially in, for example, a hydroxylamine-oxime circulating system. Specifically, the processes performed are as follows: using phosphate as inorganic process liquor to catalytically reduce nitrate ions to hydroxylamine from nitric acid and hydroxylamine as raw materials (see equation [I] below); reacting the resultant hydroxylamine with cyclohexanone in an oximation reaction to form cyclohexane oxime (see equation [II] below); adding nitric acid to the resultant inorganic process liquor or adsorbing nitrous gas to form nitric acid in the resultant inorganic phosphate process liquor, to increase the amount of the nitrate ions needed (see equation [III] below), before entering into a hydroxylamine reactor to prepare hydroxylamine. The above processes are repeatedly performed.
Hydroxylamine ReactionNH4NO3+2H3PO4+3H2→NH3OH.H2PO4+NH4H2PO4+2H2O  [I]Oximation ReactionNH3OH.H2PO4+C6H10O→C6H10NOH+H2O+H3PO4  [II]Formation of a Nitrate IonHNO3+H2PO4−→NO3−+H3PO4  [III]
GB1387725 has disclosed a palladium-platinum alloy catalyst used can catalyze hydroxylamine reactions, thereby increasing the reaction activity. However, a downside of using the catalyst was that as the amount of platinum increased, the activity and selectivity of the reaction decreased due to the halogen-containing platinum compound (H2PtCl6) being used as the source of platinum, thereby poisoning the catalyst by halogen ions.
WO98/18717 has disclosed a palladium-platinum catalyst composition, wherein the weight ratio of palladium and platinum ranged from 6:4 to 9.9:0.1, and preferably ranged from 7:3 to 9.5:0.5. Although the activity of hydroxylamine reaction can be increased by adding the aforesaid catalyst, the selectivity for the hydroxylamine was too low due to the excessive amount of platinum present in the catalyst.
In light of the above, it is clear that as the conventional catalyst compositions for catalyzing hydroxylamine reaction increased yields of hydroxylamine by increasing their catalytic activity, selectivity for the catalysts was reduced, thereby increasing consumptions of the catalyst compositions. Accordingly, it is desirable to develop a catalyst composition with high catalytic activity and selectivity.